Update core WGL function signatures to match wingdi.h

[cstanfill]

See issue #525

After this change my loader generates identical declarations to wingdi.h Reference DescribePixelFormat https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-describepixelformat wglDescribeLayerPlane https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-wgldescribelayerplane GetEnhMetaFilePixelFormat https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-getenhmetafilepixelformat wglGetLayerPaletteEntries https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-wglgetlayerpaletteentries

[oddhack]

LGTM. Since we aren't publishing a WGL core header I'm not concerned about the change.

[oddhack]

@pdaniell-nv do you want to move this to Signed Off status?